The Mars Microphone: Ready To Go

by Greg Delory

Ever wonder what it sounds like on Mars? When the next lander in NASA's
program to explore the Red Planet touches down in 1999, we will all have
the chance to find out. Onboard the Mars Polar Lander will be a small
recording device, the Mars Microphone, whose job is to sample sound while
the rest of the probe studies the soil, weather, and atmospheric dust.

Mars Microphone
Photo by Robin Weiner of the Associated Press

The idea for the Mars Microphone started with Janet Luhmann of the
University of California, Berkeley and David Juergens of the Jet Propulsion
Laboratory, who proposed to the Planetary Society that a sound-recording
device would be easy to include on a Mars mission. Society Executive
Director Louis Friedman investigated the possibility of incorporating a
microphone in the Mars Polar Lander mission.

At that time, mission planners had just selected a Russian instrument to be
put aboard the spacecraft (the first Russian instrument included on a US
planetary mission). Under the direction of Viacheslav Linkin of the Space
Research Institute in Moscow, the lidar will use a laser to study the
distribution of dust in the Martian atmosphere. Linkin offered a place on
the lidar for the microphone, which could operate without requiring any
mass, power, volume, or data-rate adjustments on the lander.

Friedman and Society President Carl Sagan then requested NASA approval to
include the microphone in the Mars Polar Lander payload, stipulating that
there would be no cost to NASA. NASA Associate Administrator for Space
Science Wes Huntress agreed.

The Planetary Society formed a team with the Space Sciences Laboratory at
Berkeley, and together we developed a low-cost implementation plan that
enabled us to build the instrument with funding solely by the Planetary
Society.

The Mars Microphone will be the first instrument funded by a membership
organization to fly to another world. It was designed, constructed, and
tested under Luhmann's direction at the Space Sciences Laboratory.

Are There Sounds on Mars?

Given that sound waves need an atmospheric medium through which to travel,
many people are surprised to learn that any sounds at all can be heard on
Mars. The atmospheric pressure on the surface of the Red Planet is small,
amounting to around 0.1 percent of the Earth's sea level pressure. But even
at Mars' low pressure, acoustic signals within the frequency range of the
human ear can be detected. And while the atmosphere of Mars is very
different from Earth's, consisting mostly of carbon dioxide, there are
similarities between these environments that should make the sound data
worthwhile.

For example, there is weather on Mars, including winds, sandstorms, and
dust devils, which are little tornadoes caused by local weather patterns.
The Mars Microphone may be able to hear these winds and perhaps even a type
of lightning within sandstorms. The microphone will also record noises made
by the lander, such as the sound of the robotic arm digging for soil
samples.

However, the most exciting sounds are likely to be ones that we don't even
know about yet. Experience has demonstrated that whenever a new instrument
is developed and flown in space, we learn something new about
extraterrestrial environments, and therein lies the true spirit of the
Mars Microphone concept.

The instrument will bring the public closer to Mars exploration. The sounds
picked up by the Mars Microphone will be available on a World Wide Web page
during the mission so that anyone will be able to hear for themselves what
it sounds like on Mars.

Building and Testing on a Shoestring

The Mars Microphone is a small device, roughly 5 centimeters on a side and
one centimeter thick (2 x 2 x 0.5 inches), weighing less than 50 grams (1.8
ounces) and using a small amount of power, less than 0.1 watt during its
most active times. In addition to the microphone, the instrument contains
digital electronics to acquire and store sound samples. Because the rate at
which we can acquire data will be limited, it will take several days, maybe
even a week, to retrieve one 10-second sound clip. The device has internal
memory, similar to the RAM in your home computer, which will store sounds
for transmission to Earth along with other lander data.

In the construction of the Mars Microphone, we relied on commercial,
off-the-shelf technology, meaning that very few of the components were
developed specifically for this mission. Most are readily available
commercially. Our sound processor chip, for example, is also used in
talking toys and educational computers that listen and respond to spoken
words. The microphone itself is typically used in hearing aids. The entire
program, including design, construction, and testing, cost roughly $50,000,
a bargain for an instrument on a planetary probe.

The Mars Microphone has since passed several tests to show it can withstand
the rigors of a planetary mission. Radiation levels in space and on Mars
are higher than what we are used to on Earth, and, like humans, the
electronic components in the microphone are sensitive to radiation damage.
We exposed the microphone and the sound processor chip to levels of
radiation that they would receive during the mission, and there were no
failures or degradation of performance. We also conducted thermal tests
with temperature ranges of -100 to +20 degrees Celsius (about -150 to +70
degrees Fahrenheit), and detected no malfunctions.

Finally, we performed pressure tests to ensure that the microphone could
actually hear noises at the low pressures of the Martian atmosphere.
Although sound level diminishes substantially with decreased pressures, we
were still able to hear sounds by increasing the gain of the amplifiers
within the microphone.

The microphone was integrated onto the Mars Polar Lander last October at
Lockheed Martin in Denver, Colorado. We verified that the microphone worked
properly on the lander and even listened to the technicians conversing as
they tended to the craft.

The next phase of testing will occur this summer, when the entire lander
plus microphone will undergo thermal and vacuum tests to simulate the
journey through space and operations on the Martian surface. During this
time the microphone will practice listening to the movements of the
lander's robotic arm.

For the latest on the Mars Microphone project and more details about the
experiment, visit the Mars Microphone home page at
http://sprg.ssl.berkeley.edu/marsmic.

Greg Delory is a Postdoctoral Physicist at the Space Sciences Laboratory of
the University of California, Berkeley.

For more information on the Mars Microphone, please visit this website: